Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
In soft handover, radio links (e.g., for the Dedicated Physical Channel (DPCH)) are added and removed in a way that a mobile station always keeps at least one radio link to the UTRAN. Soft handover is generally performed by means of macro diversity, which refers to the condition that several radio links are active at the same time. In a UMTS network, soft handover can be used when cells operated on the same frequency are changed. During soft handover, a mobile station is in the overlapping cell coverage area of two sectors or cells belonging to different base stations. Therefore, the communication between the mobile station and the base stations takes place concurrently via two air interface channels from each base station separately.
As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.